I built the copper manifold/5 gallon beverage cooler tun about a two months ago. After three batches, I have to say that it is working better than I would have expected. It really works well in preventing grain from getting stuck in the plumbing and yields pretty effective extractions.

I designed my with a square configuration. Not exactly as John Palmer (howtobrew.com) suggests, but in the following configuration (hope the line draw characters show up correct on your browers):

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I used 3/4" copper tubing, elbows and 3-way joints to build the thing. However, I would recommend using 1/2" or 3/8" instead as it will be easier to run through the existing spigot hole and whatever spigot you use.

The biggest problem was cutting manifold slits in the tubing. I used a dremel tool with good success.

Also, how deep the slots have to be ? I mean, do you cut until there is a tiny opening or you cut something like half the pipe ? I guess it must change the efficiency to stop the grain particles and to only allow wort to drain into the manifold.

I slotted both the horizontal and vertical--basically any free space on the straight tubing. I also cut one slot on two of the four elbows and the two main T junctions. I wound up slotting 180 degrees around (1/2 the circumference). Not sure if less or more is best, but it seems to do the job for me. I chose not to cut any slots that were too close to the wall of the cooler as this would likely promote the liquid to flow down the sides of the inside cooler rather than filtering thru the dense grain bed.

I would recommend getting a variable flow spigot to connect to the manifold. As howtobrew.com recommends, you will get better extraction and less chance of stuck lauter if you can slow the lautering of wort down to approx. 1 qt per minute.

Having said all this, most people I have talked to are using the false bottom rather than manifold approach. I have no basis on which to compare the two approaches, but a Phil's false bottom would likely be an easier (and possibly cheaper) route to go.

I'll check this out and see if the false-bottom option would be cheaper vs. efficiency. I'm a DIY so I think I'll go with the manifold anyway :)

One more question, what is the maximum lbs of grain you can do with your 5 gal cooler ? I'd like to buy a cooler that will allow me to do 9 lbs beers as well as 19 lbs beers with proper grainbed depth, and just enough room for the mash water. So what is your maximum in a 5 gal cooler (@ 1.5 qt/lb) ?

The 5 gallon tun is really suited for 5 gallon batch of ale. Assuming you are doing a single infusion mash, you can comfortably house around 11 pounds of grain + strike water. Any larger batches, I would look at the 10 gallon cooler . . .